The assessment of respiratory mechanics in animal models of respiratory disease is bound by a phenotyping uncertainty principle which balances measurement precision against noninvasiveness. The method that currently represents the ultimate in precision is the measurement of input impedance using the forced oscillation technique in anesthetized, paralyzed, tracheostomized animals. At the other extreme, the least invasive (but also least specific method) is unrestrained plethysmography in conscious animals. Intermediate between these two methods is the measurement of transfer impedance in conscious but restrained animals. Although the application of these methods presents special problems in mice on account of their small size, all methods have been applied previously in this species. Nevertheless, each method has yet to be developed to its full potential in mice. Furthermore, it is not fully understood how the various mechanics estimates provided by these three methods relate to each other. The goal of this proposal is to extend the capabilities of these three methods in mice and to compare their respective measures of respiratory mechanics. We will pursue three specific aims: 1) to obtain respiratory mechanics and thoracic gas volume in mice by the simultaneous measurement of input and transfer impedances using forced oscillations in tracheal flow, 2) to compare and contrast the measures or respiratory mechanics provided by conscious transfer impedance to those of anesthetized, paralyzed, tracheostomized input/transfer impedance, and 3) to condition the inspired gas during unrestrained plethysmography in mice so that gas heating and humidification effects are eliminated from the box pressure variations measured during spontaneous breathing in order to develop a noninvasive approach to assessing respiratory mechanics. The proposed work is expected to result in a set of optimized measurement tools for assessing lung function in mice. These tools will span the phenotyping uncertainty spectrum, giving researchers maximum flexibility in choosing a tool appropriate for a given application. This should have significant impact on research into mouse models of respiratory disease.